The present specification relates to displays. More particularly, the present specification relates to head up displays (HUDs).
Conventional HUDs are generally large, expensive and difficult to fit into small airplanes. Often, conventional HUDs rely on large lenses to form adequate field of view and viewing eye box. Compact HUDs are needed for small business jets and other aircraft where space is constrained in the cockpit.
Substrate guided HUDs have been proposed which use waveguide technology with diffraction gratings to preserve eye box size while reducing lens size. U.S. Pat. No. 4,309,070 issued St. Leger Searle and U.S. Pat. No. 4,711,512 issued to Upatnieks disclose substrate guided HUDS. However, such systems have faced difficulties in design. For example, diffraction gratings based upon holographic materials can be difficult to process consistently. Holograms are generally extremely angle- and wavelength-sensitive because they rely on low index modulation throughout a thick volume (Δn<0.05), where the required phase shift for diffraction can only be met for a small set of wavelengths and angles. Diffraction gratings fabricated using embossing and casting processes are more repeatable but can be limited to organic low refractive index materials, thereby limiting the field of view and spectral range. Diffraction gratings that have mechanically reproduced gratings (ruled gratings) often do not achieve the required resolution for HUD applications.
Therefore, there is a need for diffraction gratings optimized for HUD applications. Yet further, there is need a substrate waveguide HUD including diffraction gratings that meet performance and cost requirements. Still further, there is a need for a HUD including substrate waveguide with diffraction gratings that can be fabricated with sufficient repeatability on a substrate material with acceptable optical characteristics. Yet further, there is a need for a HUD substantive including high index of refraction substantive waveguide with diffraction ratings that enables wide field of view and acceptable luminance.